"Postmenopausal syndrome" is a term used to describe various pathological conditions which frequently affect women who have entered into or completed the physiological metamorphosis known as menopause. Although numerous pathologies are contemplated by the use of this term, three major medical conditions of postmenopausal syndrome are the source of the greatest long-term medical concern: osteoporosis, cardiovascular effects such as hyperlipidemia, and estrogen-dependent cancer such as breast and uterine cancer.
Osteoporosis, which generally includes a group of disorders which arise from diverse etiologies, is characterized by the net loss of bone mass per unit volume.
The consequence of this loss of bone mass and resulting bone fracture is the failure of the skeleton to provide adequate structural support for the body. One of the most common types of osteoporosis is that associated with menopause. Most women lose from about 20% to about 60% of the bone mass in the trabecular compartment of the bone within three to six years after the cessation of menses. This rapid loss is generally associated with an increase of bone resorption and formation. However, the resorptive cycle is more dominant and the result is a net loss of bone mass.
Osteoporosis is a common and serious disease among postmenopausal women. There are an estimated 25 million women in the United States who are afflicted with this disease. The results of osteoporosis disease's sequelae are personally harmful and often result in the need for extensive and long term medical support (hospitalization and nursing home care). This is especially true in elderly patients. Additionally, although osteoporosis is not generally thought of as a life threatening condition, a 20% to 30% mortality rate is related with hip fractures in elderly women. A large percentage of this mortality rate can be directly associated with postmenopausal osteoporosis.
The trabecular tissue is the most vulnerable bone tissue to the effects of postmenopausal osteoporosis. This tissue is often referred to as spongy or cancellous bone and is particularly concentrated near the ends of the bone (near the joints) and in the vertebrae of the spine. The trabecular tissue is characterized by small osteoid structures which inter-connect with each other, as well as the more solid and dense cortical tissue which makes up the outer surface and central shaft of the bone. This interconnected network of trabeculae gives lateral support to the outer cortical structure and is critical to the biomechanical strength of the overall structure. In postmenopausal osteoporosis, it is loss of the trabeculae which leads to the failure and fracture of bone. In light of the loss of the trabeculae in postmenopausal women, it is not surprising that the most common fractures are those associated with bones which are highly dependent on trabecular support, e.g., the vertebrae and the neck of the weight bearing bones, such as the femur and the fore-arm. Indeed, hip fracture, collies fractures, and vertebral crush fractures are hallmarks of postmenopausal osteoporosis.
At this time, the generally accepted method for treatment of postmenopausal osteoporosis is estrogen replacement therapy (ERT). Although ERT is generally successful, patient compliance with this therapy is low primarily because estrogen treatment frequently produces undesirable side effects.
Prior to menopause, most women have less incidence of cardiovascular disease than age-matched men. Following menopause, however, the rate of cardiovascular disease in women, such as hyperlipidemia, increases to match the rate seen in men. This rapid increase in the incidence of cardiovascular disease has been linked, in part, to the loss of estrogen and to the loss of estrogen's ability to regulate serum lipids. The nature of estrogen's ability to regulate serum lipids is not well understood, but evidence to date indicates that estrogen can upregulate the low density lipid (LDL) receptors in the liver to remove excess cholesterol. Additionally, estrogen appears to have some effect on the biosynthesis of cholesterol, as well as other beneficial effects on cardiovascular health.
It has been reported in the literature that postmenopausal women undergoing estrogen replacement therapy have a return of serum lipid levels to concentrations similar to those of the premenopausal state. Thus, estrogen would appear to be a reasonable treatment for this condition. However, the side-effects of ERT are not acceptable to many women, thus limiting the use of this therapy. An ideal therapy for this condition would be an agent which would regulate the serum lipid levels like estrogen, but would be devoid of the side-effects and risks associated with estrogen therapy.
The third major pathology associated with, but not limited to, postmenopausal syndrome is estrogen-dependent cancer, primarily breast and uterine cancer. Although such neoplasms are not solely limited to postmenopausal women, they are more prevalent in the older postmenopausal population. Current chemotherapy of these cancers has relied heavily on the use of estrogen agonist/antagonist compounds, such as tamoxifen. Although such mixed agonist/antagonists have beneficial effects in the treatment of these cancers, the estrogenic side-effects are tolerable in only acute life-threatening situations. These agents have stimulatory effects on certain cancer cell populations in the uterus due to their estrogenic (agonist) properties and therefore, are contraproductive in some cases. A better therapy for the treatment of these cancers would be an agent which is an antiestrogenic compound in cancerous tissue, having negligible or no estrogen agonist properties on other reproductive tissues.
In response to the clear need for new pharmaceutical agents which are capable of alleviating the symptoms of, inter alia, postmenopausal syndrome, the present invention provides new compounds, pharmaceutical compositions thereof, and methods of using such compounds for the treatment of postmenopausal syndrome and other estrogen-related pathological conditions such as those mentioned herein.